Atomic layer deposition using metal amidinates

ABSTRACT

Metal films are deposited with uniform thickness and excellent step coverage. Copper metal films were deposited on heated substrates by the reaction of alternating doses of copper(I) NN′-diispropylacetamidinate vapor and hydrogen gas. Cobalt metal films were deposited on heated substrates b the reaction of alternating doses of cobalt(II) bis(N,N′-diispropylacetamidinate) vapor and hydrogen gas. Nitrides and oxides of these metals can be formed by replacing the hydrogen with ammonia or water vapor, respectively. The films have very uniform thickness and excellent step coverage in narrow holes. Suitable applications include electrical interconnects in microelectronics and magnetoresistant layers in magnetic information storage devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the earlier filing date of U.S.patent application Ser. No. 12/496,499, filed Jul. 1, 2009; which is aDivisional of U.S. patent application Ser. No. 10/534,687, now U.S. Pat.No. 7,557,229; which is a U.S. National Stage Application ofInternational Application No. PCT/US2003/036568, filed Nov. 14, 2003;which is an application claiming the benefit under 35 USC 119(e) of U.S.Provisional Patent Application No. 60/463,365 filed Apr. 16, 2003 andU.S. Provisional Patent Application No. 60/426,975 filed Nov. 15, 2002,all of which are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to materials and processes for deposition ofconformal films containing metals on solid substrates, and inparticular, to films including copper, cobalt and iron metals or theiroxides or nitrides. This invention may be applied to the fabrication ofmicroelectronics devices.

2. Description of the Related Art

As the speed and functionality of semiconductor microelectronic devicesare improved, new materials are needed. For example, materials withhigher electrical conductivity are needed to form the wiring betweentransistors in integrated circuits. Copper has higher electricalconductivity and better stability against electro-migration than doesaluminum. Therefore, copper is becoming more commonly used in siliconsemiconductors. This trend is described in the International TechnologyRoadmap for Semiconductors, published on the Internet athttp://public.itrs.net/Files/2001ITRS/Home.htm.

Copper interconnections must also be disposed conformally in structures,such as narrow holes, and the resulting films must have highly uniformthickness. If there are variations in thickness, the electricalconductivity of the copper in a trench or via is degraded because ofincreased electron scattering from the rough surface of the copper. Thushigh-quality barrier/adhesion layers desirably have very smoothsurfaces.

One method that is suitable for making smooth, conformal layers is“atomic layer deposition”, or ALD (also known as atomic layer epitaxy).The ALD process deposits thin layers of solid materials using two ormore different vapor phase precursors. The surface of a substrate ontowhich film is to be deposited is exposed to a dose of vapor from oneprecursor. Then any excess unreacted vapor from that precursor is pumpedaway. Next, a vapor dose of the second precursor is brought to thesurface and allowed to react. This cycle of steps can be repeated tobuild up thicker films. One particularly important aspect of thisprocess is that the ALD reactions are self-limiting, in that only acertain maximum thickness can form in each cycle, after which no furtherdeposition occurs during that cycle, even if excess reactant isavailable. Because of this self-limiting character, ALD reactionsproduce coatings with highly uniform thicknesses. Uniformity of ALD filmthicknesses extends not only over flat substrate surfaces, but also intonarrow holes and trenches. This ability of ALD to make conformal filmsis called “good step coverage.”

ALD of copper has been demonstrated from the copper precursorCu(II)-2,2,6,6-tetramethyl-3,5-heptanedionate by P. Martensson and J.-O.Carlsson in the Journal of the Electrochemical Society, volume 145,pages 2926-2931 (1998). Unfortunately, copper from this ALD process onlygrows on pre-existing platinum surfaces, and does not nucleate or adhereto most other surfaces in the temperature range (<200° C.) in whichthere is a true self-limiting ALD process. Other reactions have beensuggested for ALD of copper, but no data have been published todemonstrate that the proposed surface reactions are actuallyself-limiting. Therefore it would be highly advantageous to have an ALDprocess for copper that nucleates and adheres to surfaces other thanplatinum.

U.S. Pat. No. 6,294,836 reports improvement in the adhesion of copper byuse of a “glue” layer of cobalt between the copper and a substrate.However, known chemical vapor deposition (CVD) techniques for depositingcobalt have poor step coverage, giving only 20% thickness at the bottomof a hole with aspect ratio 5:1, according to U.S. Pat. No. 6,444,263.ALD of cobalt has been claimed in US Patent Application No. 2002/0081381for the reaction of cobalt bis(acetylacetonate) [Co(acac)₂] withhydrogen, but no step coverage data were given and growth was seen onlyon pre-existing iridium surfaces. US Patent Application No. 2002/0081381also claims non-selective growth of cobalt by the reaction of Co(acac)₂with silane, but this cobalt may be contaminated with silicon. Thus itwould be advantageous to have a deposition process for pure cobalthaving high step coverage.

Thin layers of copper and cobalt are also used to form magnetoresistantwrite and read heads for magnetic information storage. These layers needto have very uniform thicknesses and very few defects or pinholes. Whilesuccessful commercial processes exist for making these devices, it wouldbe advantageous to have deposition processes for copper and cobalt thatproduced layers with more uniform thickness and fewer defects.

Advanced designs for magnetic memory integrated with microelectroniccircuits (see, for example, US Patent Application No. 2002/0132375 andU.S. Pat. No. 6,211,090) call for highly uniform and conformal layers ofmetals (particularly Fe, Co, Ni, Cu, Ru, Mn) with tightly controlledthickness and sharp interfaces. There are no known methods fordepositing these metal layers with the required conformality and controlof thickness.

SUMMARY OF THE INVENTION

One aspect of the present invention includes a process for depositingfilms comprising metals such as copper, cobalt, nickel, iron, ruthenium,manganese, chromium, vanadium, niobium, tantalum, titanium or lanthanumusing a volatile metal amidinate compound. The films have uniform,conformal thicknesses and smooth surfaces.

An advantage of this process is its ability to form metal-containingcoatings with extremely uniform thickness.

A related aspect of the present invention is the deposition ofmetal-containing coatings under conditions that produce good adhesionbetween substrates and the deposited coating.

An advantage of the process is that it permits deposition ofmetal-containing coatings with extremely smooth surfaces.

An additional advantage of the process is the vapor deposition of highlyuniform metal-containing coatings is accomplished over a range ofconditions such as concentrations of reactants and position of thesubstrate inside the reactor.

Another advantage of the invention is its ability to make conformalmetal-containing coatings of over substrates with narrow holes, trenchesor other structures. This ability is commonly known as “good stepcoverage.”

Another aspect of the present invention is the preparation ofmetal-containing coatings that are substantially free of pin-holes orother mechanical defects.

Another advantage of the invention is the ability to depositmetal-containing coatings with high electrical conductivity.

Another advantage of the invention is the ability to depositmetal-containing coatings that adhere strongly to oxide substrates.

Another advantage of the invention includes the ability to coatsubstrates with metal-containing coatings at relatively lowtemperatures.

A further aspect of the invention includes a process for atomic layerdeposition of metal-containing coatings without plasma damage tosubstrates.

One particular aspect of the present invention includes a process fordepositing electrically conductive copper coatings for use as connectorsin microelectronic devices.

Another particular aspect of the present invention includes a processfor depositing cobalt coatings having useful magnetic properties.

An additional aspect of the invention is the deposition of a cobaltlayer and then a copper layer on a diffusion barrier (such as TiN, TaNor WN) in a microelectronic interconnect structure.

A further aspect of the present invention includes a process fordepositing cobalt/copper nanolaminate coatings having usefulmagneto-resistance properties.

In one aspect of the present invention, a thin film comprising a metalis prepared by exposing a heated substrate alternately to the vapor ofone or more volatile metal amidinate compounds (M-AMD), and then to areducing gas or vapor, to form a metal coating on the surface of thesubstrate. In one or more embodiments, the reducing gas includeshydrogen.

In one aspect of the invention, a thin film comprising a metal nitrideis prepared by exposing a heated substrate alternately to the vapor ofone or more volatile metal amidinate compounds (M-AMD), and then to anitrogen-containing gas or vapor, to form a metal nitride coating on thesurface of the substrate. In one or more embodiments, thenitrogen-containing gas includes ammonia.

In another aspect of the invention, a thin film comprising a metal oxideis prepared by exposing a heated substrate alternately to the vapor ofone or more volatile metal amidinate compounds (M-AMD), and then to anoxygen-containing gas or vapor, to form a metal oxide coating on thesurface of the substrate. In one or more embodiments, theoxygen-containing gas includes water.

In one or more embodiments, the volatile metal amidinate compound is ametal amidinate compound having a formula selected from the groupconsisting of M(I)AMD, M(II)AMD₂ and M(III)AMD₃ and oligomers thereof,where M is a metal and AMD is an amidinate moiety.

In one aspect of the invention vapors of a volatile copper compound arereacted alternately with hydrogen gas at a surface to produce thinlayers of copper metal on the surface. Particularly suitable coppercompounds are chosen from the class of copper(I) amidinates.

In another aspect of the invention vapors of a volatile cobalt compoundare reacted alternately with hydrogen gas at a surface to produce thinlayers of cobalt metal on the surface. Particularly suitable cobaltcompounds are chosen from the class of cobalt(II) amidinates. Replacingthe hydrogen gas in this process with ammonia gas can deposit cobaltnitride. Replacing the hydrogen gas in this process with water vapor candeposit cobalt oxide.

In other embodiments of the invention, amidinates of nickel, iron,ruthenium, manganese, chromium, vanadium, niobium, tantalum, titaniumand lanthanum are used for vapor deposition of thin films comprising oneor more of these metals.

In another aspect of the invention vapors of a volatile lanthanumcompound are reacted alternately with ammonia gas at a surface toproduce thin layers of lanthanum nitride on the surface. Particularlysuitable lanthanum compounds are chosen from the class of lanthanum(III)amidinates. Replacing the ammonia in this process with water vapor candeposit lanthanum oxide.

In some embodiments, the reaction may be carried out in a manner to formfilms on substrates that may include holes or trenches. Coatings mayalso be placed on powders, wires or around and within complicatedmechanical structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and various other aspects, features, and advantages of thepresent invention, as well as the invention itself, may be more fullyappreciated with reference to the following detailed description of theinvention when considered in connection with the following drawings. Thedrawings are presented for the purpose of illustration only and are notintended to be limiting of the invention, in which:

FIG. 1 is a cross-sectional illustration of an atomic deposition layerapparatus used in the practice of at least one embodiment of theinvention;

FIG. 2 is the molecular structure of a copper precursor used in thepractice of at least one embodiment of the invention;

FIG. 3 is the molecular structure of a cobalt precursor used in thepractice of at least one embodiment of the invention;

FIG. 4 is a cross-sectional scanning electron micrograph of narrow holeswhose walls are coated with copper metal using one embodiment of theinvention;

FIG. 5 is an optical micrograph of a narrow hole whose walls are coatedwith cobalt metal using one embodiment of the invention;

FIG. 6 is a plot of the thickness of copper deposited in each ALD cycle,as a function of substrate temperature; and

FIG. 7 is a plot of the thickness of cobalt deposited in each ALD cycle,as a function of substrate temperature.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for preparing a metal containinglayer by atomic layer deposition from reactants including metalamidinates. In an atomic layer deposition process, doses of the metalcompound vapor are supplied to a surface alternately with a vapor of asecond reactant by an apparatus such as that shown in FIG. 1, which isdescribed in detail later in this specification. Preferred metalamidinates include metal formamidinates and metal acetamidinates.Typical second reactants include hydrogen gas, ammonia gas or watervapor. When hydrogen gas is chosen as the second reactant, a metal maybe deposited. When ammonia gas is chosen as the second reactant, a metalnitride is deposited. When water vapor is chosen as the second reactant,a metal oxide is deposited.

In one or more embodiments, precursors for monovalent metals includevolatile metal(I) amidinates, [M(I)(AMD)]_(x), where x=2, 3. Some ofthese compounds have a dimeric structure 1,

in which R¹, R², R³, R^(1′), R^(2′) and R^(3′) are groups made from oneor more non-metal atoms. In some embodiments, R¹, R², R³, R^(1′), R^(2′)and R^(3′) may be chosen independently from hydrogen, alkyl, aryl,alkenyl, alkynyl, trialkylsilyl or fluoroalkyl groups or other non-metalatoms or groups. In some embodiments, R¹, R², R³, R^(1′), R^(2′) andR^(3′) are each independently alkyl or fluoroalkyl or silylalkyl groupscontaining 1 to 4 carbon atoms. Suitable monovalent metals includecopper(I), silver(I), gold(I), and iridium(I). In one or moreembodiments, the metal amidinate is a copper amidinate, and the copperamidinate comprises copper(I) N,N′-diisopropylacetamidinate,corresponding to taking R¹, R², R^(1′), and R^(2′) as isopropyl groups,and R³ and R^(3′) as methyl groups in the general formula 1. In one ormore embodiments, the metal(I) amidinate is a trimer having the generalformula [M(I)(AMD)]₃.

In one or more embodiments, divalent metal precursors include volatilemetal(II) bis-amidinates, [M(II)(AMD)₂]_(x), where x=1, 2. Thesecompounds may have a monomeric structure 2,

in which R¹, R², R³, R^(1′), R^(2′) and R^(3′) are groups made from oneor more non-metal atoms. In one or more embodiments, dimers of thisstructure, e.g., [M(II)(AMD)₂]₂, may also be used. In some embodiments,R¹, R², R³, R^(1′), R^(2′) and R^(3′) may be chosen independently fromhydrogen, alkyl, aryl, alkenyl, alkynyl, trialkylsilyl, or fluoroalkylgroups or other non-metal atoms or groups. In some embodiments, R¹, R²,R³, R^(1′), R^(2′) and R^(3′) are each independently alkyl orfluoroalkyl or silylalkyl groups containing 1 to 4 carbon atoms.Suitable divalent metals include cobalt, iron, nickel, manganese,ruthenium, zinc, titanium, vanadium, chromium, europium, magnesium andcalcium. In one or more embodiments, the metal(II) amidinate is a cobaltamidinate, and the cobalt amidinate comprises cobalt(II)bis(N,N′-diisopropylacetamidinate), corresponding to taking R¹, R²,R^(1′), and R^(2′) as isopropyl groups, and R³ and R^(3′) as methylgroups in the general formula 2.

In one or more embodiments, precursors for trivalent metals includevolatile metal(III) tris-amidinates, M(III)(AMD₃. Typically, thesecompounds have a monomeric structure 3,

in which R¹, R², R³, R^(1′), R^(2′), R^(3′), R^(1″), R^(2″) and R^(3″)are groups made from one or more non-metal atoms. In some embodiments,R¹, R², R³, R^(1′), R^(2′), R^(3′), R^(1″), R^(2″) and R^(3″) may bechosen independently from hydrogen, alkyl, aryl, alkenyl alkynyl,trialkylsilyl, halogen or partly fluorinated alkyl groups. In someembodiments, R¹, R², R³, R^(1′), R^(2′), R^(3′), R^(1″), R^(2″) andR^(3″) are each independently alkyl groups containing 1 to 4 carbonatoms. Suitable trivalent metals include lanthanum, praseodymium and theother lanthanide metals, yttrium, scandium, titanium, vanadium, niobium,tantalum, chromium, iron, ruthenium, cobalt, rhodium, iridium, aluminum,gallium, indium, and bismuth. In one or more embodiments, the metal(III)amidinate is a lanthanum amidinate, and the lanthanum amidinatecomprises lanthanum(III) tris(N,N′-di-tert-butylacetamidinate),corresponding to taking R¹, R², R^(1′), R^(2′), R^(1″) and R^(2″) astert-butyl groups and R³, R^(3′) and R^(3″) as methyl groups in thegeneral formula 3.

As used herein, metal amidinates having the same ratio of metal toamidinate as the monomer, but varying in the total number ofmetallamidinate units in the compound are referred to as “oligomers” ofthe monomer compound. Thus, oligomers of the monomer compound M(R)AMD₂include [M(II)(AMD)₂]_(x), where x is 2, 3, etc. Similarly, oligomers ofthe monomer compound M(I)AMD include [M(I)AMD]_(x), where x is 2, 3,etc.

Metal amidinates may be prepared using any suitable method. One methodto make a metal amidinate precursor involves first forming a lithiumamidinate by reaction of a 1,3-dialkylcarbodiimide with an alkyllithiumcompound:

Then the lithium amidinate is reacted with a metal halide to form ametal amidinate:

Unsymmetrical carbodiimides (in which R¹ is not the same as R²), as wellas symmetric carbodiimides (R¹=R²), can be synthesized by the followingsequence of reactions:

A wide variety of alkylamines and alkylisocyanates are commerciallyavailable to supply the R¹ and R² alkyl groups. Different R³ alkylgroups can be supplied by the use of appropriate alkyllithium compounds.

Another method for making metal amidinates uses N,N′-dialkylamidines,

rather than carbodiimides.

An amidine may be converted into a metal amidinate by reacting theamidine with a metal hydride (R=H), a metal alkyl (R=alkyl) or a metalalkylamide (R=dialkylamide):

Alternatively, this last reaction may be used to form an alkali metalsalt of the amidine, which is then subsequently reacted with a metalhalide to form the desired metal amidine.

N,N′-dialkylamidines may be synthesized by any convenient method knownin the art of organic chemistry. Symmetric amidines (R¹=R²) may beformed by condensation of amines with nitrites catalyzed by lanthanumtrifluoromethanesulfonate (also known as lanthanum triflate):

Unsymmetric amidines (R¹ not equal to R²), as well as symmetricamidines, may be synthesized by the following reactions starting from anamide. Some amides are commercially available, and others may besynthesized by reaction of an organic acid chloride with an amine:

Next, the amide is reacted with trifluoromethanesulfonic anhydride (alsoknown as triflic anhydride) in the presence of an organic base such aspyridine, to form an iminium salt:

This intermediate iminium salt is then reacted with an alkylammoniumchloride R²NH₃Cl and then with a base such as NaOH to form the desiredfree amidine:

In order to make these reactions as facile as possible, the group R² ischosen to be more sterically hindered than the R¹ group, for thesynthesis of unsymmetric amidines.

Liquid precursors generally have several advantages in practicing theinvention. If the melting point of the metal amidinate is below roomtemperature, then the liquid compound can be made in high purity byfractional distillation. In contrast, solid materials are more difficultto purify by sublimation, which is less effective than distillation inremoving impurities. Air-sensitive liquid compounds are also generallyeasier to handle and transfer than are solids.

Metal amidinates with lower melting points can be made by using longerchain alkyl groups for R¹, R² and/or R³. Unsymmetrical metal amidinates(in which R¹ is not the same as R²) generally have lower melting pointsthan symmetric metal amidinates. Alkyl groups with more than onestereoisomer, such as sec-butyl, also lead to lower melting points. Useof one or more of these strategies can lead to desirable liquidprecursors, rather than less desirable solid compounds.

Low melting points are also desirable in supplying vapor for adeposition process according to this invention. If the melting point ofa compound is lower than the temperature at which the compound isvaporized, then the liquid source of vapor generally has faster kineticsof vaporization than solid compounds have. Also, sublimation of a solidoften leaves its surface covered with a residue of less volatilematerial that impedes further vaporization. In a liquid source, on theother hand, any non-volatile residue may precipitate into the bulk ofthe liquid, leaving the liquid surface clean and capable of desirablerapid evaporation.

According to one or more embodiments of the present invention, a metalamidinate is introduced onto a substrate as a vapor. Vapors ofprecursors may be formed by conventional methods from either liquid orsolid precursors. In one or more embodiments, a liquid precursor may bevaporized by nebulization into a carrier gas preheated above thevaporization temperature, e.g., to about 100 to 200° C. The nebulizationmay be carried out pneumatically, ultrasonically, or by other suitablemethods. Solid precursors to be nebulized may be dissolved in organicsolvents, including hydrocarbons such as decane, dodecane, tetradecane,toluene, xylene and mesitylene, ethers, esters, ketones and chlorinatedhydrocarbons. Solutions of liquid precursors generally have lowerviscosities than pure liquids, so that in some cases it may bepreferable to nebulize and evaporate solutions rather than pure liquids.The precursor liquid or precursor solutions may also be evaporated withthin-film evaporators, by direct injection of the liquids or solutionsinto a heated zone, or by heating in a bubbler. Commercial equipment forvaporization of liquids is made by MKS Instruments (Andover, Mass.),ATMI, Inc. (Danbury, Conn.), Novellus Systems, Inc. (San Jose, Calif.)and COVA Technologies (Colorado Springs, Colo.). Ultrasonic nebulizersare made by Sonotek Corporation (Milton, N.Y.) and Cetac Technologies(Omaha, Nebr.).

The metal precursors of the present invention may be reacted with areducing agent, e.g., hydrogen gas, to form films of the metal. Forexample, copper(I) N,N′-diisopropylacetamidinate may be reacted withhydrogen gas to form copper metal. In other embodiments, the metalprecursors of the present invention may also be reacted with othersuitably reactive reducing compounds to form metals. In someembodiments, the metal precursors of the present invention may bereacted with ammonia gas to form metal nitrides. For example, cobalt(II)bis(N,N′-diisopropylacetamidinate) may be reacted with ammonia gas toform cobalt nitride. In other embodiments, the metal precursors of thepresent invention may be reacted with water vapor to form metal oxides.For example, lanthanum(III) tris(N,N′-di-tert-butylacetamidinate) may bereacted with water vapor to form lanthanum oxide.

The process of the invention may be carried out using atomic layerdeposition (ALD). ALD introduces a metered amount of a first reactantinto a deposition chamber having a substrate therein for layerdeposition. A thin layer of the first reactant is deposited on thesubstrate. Then any unreacted first reactant and volatile reactionby-products are removed by a vacuum pump and, optionally, a flow ofinert carrier gas. A metered amount of a second reactant component isthen introduced into the deposition chamber. The second reactantdeposits on and reacts with the already deposited layer from the firstreactant. Alternating doses of first and second reactants are introducedinto the deposition chamber and deposited on the substrate to form alayer of controlled composition and thickness. The time between dosesmay be on the order of seconds and is selected to provide adequate timefor the just-introduced component to react with the surface of the filmand for any excess vapor and byproducts to be removed from the headspaceabove the substrate. It has been determined that the surface reactionsare self-limiting so that a reproducible layer of predictablecomposition is deposited. As will be appreciated by one of ordinaryskill in the art, deposition processes utilizing more than two reactantcomponents are within the scope of the invention.

In one or more embodiments of the invention, a 6-port sampling valve(Valco model EP4C6WEPH, Valco Instruments, Houston, Tex.) normally usedfor injecting samples into gas chromatographs may be used to deliverpulses of reactant gas. Each time that the valve is turned by computercontrol, a measured volume of gas in the “sample loop” flows into thedeposition chamber. A constant flow of carrier gas helps to clearresidual reactant gas from the tube leading into the heated depositionzone. This delivery method is convenient for reactant gases such ashydrogen and ammonia.

Doses of reactants whose vapor pressures are higher than the pressure inthe deposition chamber can be introduced using apparatus such as thatillustrated in FIG. 1. For example, water has a vapor pressure (about 24Torr at room temperature) that is much higher than a typical pressure inthe deposition chamber (usually less than 1 Torr). Such a volatileprecursor 20 has vapor 30 that is introduced into the heated depositionchamber 110 by the use of a pair of air-actuated diaphragm valves, 50and 70 (Titan II model made by Parker-Hannifin, Richmond Calif.). Thevalves are connected by a chamber 60 having a measured volume V, andthis assembly is placed inside an oven 80 held at a controlledtemperature T₂. The pressure of the reactant vapor 30 in the precursorreservoir 10 is equal to the equilibrium vapor pressure P_(eq) of thesolid or liquid reactant 20 at a temperature T₁ determined by thesurrounding oven 40. The temperature T₁ is chosen to be high enough sothat the precursor pressure P_(eq) is higher than the pressure P_(dep)in the deposition chamber. The temperature T₂ is chosen to be higherthan T₁ so that only vapor and no condensed phase is present in thevalves 50 and 70 or the chamber 60. In the case of a gaseous reactant,this delivery method can also be used. The gas pressure in volume V canbe set in this case by a pressure regulator (not shown) that reduces itspressure from the pressure in the vessel storing the gaseous reactant.

Carrier gas (such as nitrogen gas) flows at a controlled rate into inlet90 in order to speed the flow of the reactants into the depositionchamber and the purging of reaction byproducts and un-reacted reactantvapor. A static mixer may be placed in the tubing 100 leading into thereactor, to provide a more uniform concentration of the precursor vaporin the carrier gas as it enters the deposition chamber 110 heated byfurnace 120 and containing one or more substrates 130. The reactionbyproducts and un-reacted reactant vapors are removed by trap 140 beforepassing into a vacuum pump 150. Carrier gas exits from exhaust 160.

In operation, valve 70 is opened so that the pressure inside chamber 60is reduced to a value P_(dep) close to that of the deposition chamber110. Then valve 70 is closed and valve 50 is opened to admit precursorvapor from precursor reservoir 10 into chamber 60. Then valve 50 isclosed so that the volume V of chamber 60 contains vapor of theprecursor at a pressure P.sub.eq. Finally, valve 70 is opened to admitmost of the precursor vapor contained in chamber 60 into the depositionchamber. The number of moles, n, of precursor delivered by this cyclecan be estimated by assuming that the vapor obeys the ideal gas law:n=(P_(eq)−P_(dep))(V/RT₁) where R is the gas constant. This expressionalso assumes that carrier gas from tube 90 does not enter chamber 60through valve 70 during the brief time that it is open to release theprecursor vapor. If mixing of carrier gas with the precursor vapor doesoccur during the time that valve 70 is open, then a larger dose ofprecursor vapor may be delivered, up to a maximum valuen=(P_(eq))(V/RT₁) if all the residual precursor vapor in chamber 60 isdisplaced by carrier gas. For precursors with relatively high vaporpressure (P_(eq)>>P_(dep)), there is usually not much difference betweenthese two estimates of the precursor dose.

This cycle of delivering precursor 20 is repeated if necessary until therequired dose of precursor 20 has been delivered into the reactionchamber. Typically, in an ALD process, the dose of precursor 20delivered by this cycle (or several such cycles repeated to give alarger dose) is chosen to be large enough to cause the surface reactionsto go to completion (also called “saturation”).

In the case of precursors with vapor pressure so low that P_(eq) is lessthan P_(dep), the methods described above will not deliver any precursorvapor into the deposition chamber. The vapor pressure can be increasedby raising the temperature of the reservoir, but in some cases a highertemperature would result in thermal decomposition of the precursor.Metal amidinate precursors often have vapor pressures that are less thanthe operating pressure in the deposition chamber. In the case of athermally sensitive precursor 21 with low vapor pressure, its vapor 31may be delivered using the apparatus in FIG. 1. The chamber 19 is firstpressurized with carrier gas delivered through tube 15 and valve 17 froma pressure controller (not shown). Valve 17 is then closed and valve 51opened to allow the carrier gas to pressurize precursor reservoir 11 topressure P_(tot). The mole fraction of precursor vapor in the vaporspace 31 of reservoir 11 is then P_(eq)/P_(tot). Valve 51 is closed andthen valve 71 opened to deliver the dose of reactant vapor 31. IfP_(tot) is set to a pressure larger than the pressure P.sub.dep in thedeposition chamber, then the number of moles delivered in a dose can beestimated from the equationn=(P_(eq)/P_(tot))(P_(tot)−P_(dep))(V/RT_(1′)), where V is the volume ofthe vapor space 31 in chamber 11 and T_(1′) is the temperaturemaintained by oven 41. Oven 81 is maintained at a temperature T_(2′)that is high enough above T_(1′) to avoid condensation. If carrier gasfrom tube 91 enters the volume 31 during the time that the valve 71 isopen, then a dose somewhat larger than this estimate may be delivered.By making the volume V large enough, a precursor dose that is certainlylarge enough to saturate the surface reaction may be delivered. If thevapor pressure P_(eq) is so low that the required volume V would beimpracticably large, then additional doses from volume V may bedelivered before delivering a dose of the other reactant.

In one or more embodiments, the apparatus of FIG. 1 may include twodelivery chambers that are alike, e.g., both are used to deliver sampleshaving vapor pressures higher than or lower than the depositionpressure.

In an isothermal deposition zone 110, material is generally deposited onall surfaces exposed to the precursor vapors, including substrates andthe interior chamber walls. Thus it is appropriate to report theprecursor doses used in terms of moles divided by the total area of thesubstrates and exposed chamber walls. In some cases, deposition alsooccurs on part or all of the back side of the substrates, in which casethat area should also be included in the total area.

The invention may be understood with reference to the following exampleswhich are for the purpose of illustration only and which are notlimiting of the invention, the full scope of which is set forth in theclaims that follow.

All reactions and manipulations described in these examples wereconducted under a pure nitrogen atmosphere using either an inertatmosphere box or standard Schlenk techniques. Tetrahydrofuran (THF),ether, hexanes and acetonitrile were dried using an InnovativeTechnology solvent purification system and stored over 4 Å molecularsieves. Sec-butylamine was dried by distillation from barium oxide.Methyllithium, tert-butyllithium, 1,3-diisopropylcarbodiimide,1,3-di-tert-butylcarbodiimide, CuBr, AgCl, CoCl₂, NiCl₂, MnCl₂, MgCl₂,SrCl₂, TiCl₃, VCl₃, BiCl₃, RuCl₃, Me₃Al (trimethylaluminum), (CF₃SO₃)₃La(La triflate), La and Pr were used as received from Aldrich ChemicalCompany. The metal compounds produced by these procedures generallyreact with moisture and/or oxygen in the ambient air, and should bestored and handled under an inert, dry atmosphere such as pure nitrogenor argon gas.

EXAMPLE 1 Synthesis of (N,N′-diisopropylacetamidinato)copper([Cu(^(i)Pr-AMD)]₂)

A solution of methyllithium (1.6 M in ether, 34 mL, 0.054 mol) in etherwas added dropwise to a solution of 1,3-diisopropylcarbodiimide (6.9 g,0.055 mol) in 100 mL of ether at −30° C. The mixture was warmed up toroom temperature and stirred for 4 h. The resultant colorless solutionwas then added to a solution of copper bromide (7.8 g, 0.054 mol) in 50mL of ether. The reaction mixture was stirred for 12 h under theexclusion of light. All volatiles were then removed under reducedpressure, and the resulting solid was extracted with hexanes (100 mL).The hexanes extract was filtered through a pad of Celite on a glass fritto afford a pale yellow solution. Concentration of the filtrate andcooling it to −30° C. afforded 9.5 g of colorless crystals as a product(83%). Sublimation: 70° C. at 50 mTorr. ¹H NMR (C₆D₆, 25° C.): 1.16 (d,12H), 1.65 (s, 3H), 3.40 (m, 2H). Anal. Calcd for C₁₆H₃4N₄Cu₂: C, 46.92;H, 8.37; N, 13.68. Found: C, 46.95; H, 8.20; N, 13.78.

A [Cu(^(i)Pr-AMD)]₂ crystal was structurally characterized by X-raycrystallography. [Cu(^(i)Pr-AMD)]₂, shown in FIG. 2, is a dimer in thesolid state in which amidinate ligands bridge copper metal atoms in aμ,η¹: η¹-fashion. The average Cu—N distance is 1.860(1) Å. Thegeometries of the five-membered rings of Cu—N—C—N—Cu are planar withcentrosymmetryimposed by the crystal structure.

EXAMPLE 2 Synthesis of bis(N,N′-diisopropylacetamidinato)cobalt([Co(^(i)Pr-AMD)₂])

This compound was obtained in a similar manner as described for[Cu(^(i)Pr-AMD)], but with a 1:1 mixture of ether and THF as solvent.Recrystallization in hexanes at −30° C. gave dark green crystals asproduct (77%). Sublimation: 40° C. at 50 mTorr. m.p.: 72° C. Anal. Calcdfor C₁6H₃₄N₄Co: C, 56.29; H, 10.04; N, 16.41. Found: C, 54.31; H, 9.69;N, 15.95.

Co(^(i)Pr-AMD)₂, shown in FIG. 3, is monomeric with two amidinateligands arranged about each cobalt atom in a distorted tetrahedralenvironment. The average Co—N distance is 2.012(8) Å. The Co—N—C—Nfour-membered rings are planar with an imposed mirror plane.

EXAMPLE 3 Synthesis of cobalt bis(N,N′-di-tert-butylacetamidinate)([Co(^(t)Bu-AMD)₂])

This compound was obtained in a manner similar to ([Co(^(i)Pr-AMD)₂]) inExample 2, using 1,3-di-tert-butylcarbodiimide in place of1,3-diisopropylcarbodiimide. Dark blue crystals (84%). Sublimation: 45°C. at 50 mtorr. m.p.: 90° C. Anal. Calcd for C₂0H₄₂N₄Co: C, 60.43; H,10.65; N, 14.09. Found: C, 58.86; H, 10.33; N, 14.28.

EXAMPLE 4 Synthesis of lanthanum tris(N,N′-diisopropylacetamidinate)([La(^(i)Pr-AMD)₃])

Following a similar procedure as described above for [Co(^(i)Pr-AMD)₂],but using LaCl₃(THF)₂ in place of CoCl₂, off-white solids were obtainedas a product by sublimation of the crude solid material. Sublimation:80° C. at 40 mtorr. ¹H NMR (C₆D₆, 25° C.): 1.20 (d, 36H), 1.67 (s, 18H),3.46 (m, 6H). Anal. Calcd for C₂₄H₅₁N₆La: C, 51.24; H, 9.14; N, 14.94.Found: C, 51.23; H, 8.22; N, 14.57.

EXAMPLE 5 Synthesis of lanthanumtris(N,N′-diisopropyl-2-tert-butylamidinate)([La(^(i)Pr-^(t)BuAMD)₃].½C₆H₁₂)

Following a similar procedure as described above for [Co(^(i)Pr-AMD)₂],but using LaCl₃(THF)₂, off-white solids were obtained as a product bysublimation of the crude solid materials. Colorless crystals (80%).Sublimation: 120° C. at 50 mtorr. m.p.: 140° C. ¹H NMR (C₆D₆, 25° C.):1.33 (br, 21H), 4.26 (m, 6H). Anal. Calcd for C₃₃H₇₅N₆La: C, 57.04; H,10.88; N, 12.09. Found: C, 58.50; H, 10.19; N, 11.89.

EXAMPLE 6 Synthesis of bis(N,N′-diisopropylacetamidinato)iron([Fe(^(i)Pr-AMD)₂]₂)

Following a similar procedure as described above for [Co(^(i)Pr-AMD)₂],but using FeCl₂, yellow-green solids [Fe(^(i)Pr-AMD)₂]₂ were obtained asa product upon evaporation of the solvent from the hexanes extract.Sublimation: 70° C. at 50 mtorr. m.p.: 110° C.

EXAMPLE 7 Synthesis of iron bis(N,N′-di-tert-butylacetamidinate)([Fe(^(t)Bu-AMD)₂])

Following a similar procedure as described above for [Fe(^(i)Pr-AMD)₂]₂,but using 1,3-di-tert-butylcarbodiimide in place of1,3-diisopropylcarbodiimide, white crystals (77%) were obtained.Sublimation: 55° C. at 60 mtorr. m.p.: 107° C. Anal. Calcd forC₂₀H₄₂N₄Fe: C, 60.90; H, 10.73; N, 14.20. Found: C, 59.55; H, 10.77; N,13.86.

EXAMPLE 8 Synthesis of bis(N,N′-diisopropylacetamidinato)nickel([Ni(^(i)Pr-AMD)₂])

Following a similar procedure as described in Example 2 for[Co(^(i)Pr-AMD)₂], but using NiCl₂, and refluxing the reaction mixtureovernight, brown solids [Ni(^(i)Pr-AMD)₂] were obtained as a productupon evaporation of the solvent from the hexanes extract. Brown crystals(70%). Sublimation: 35° C. at 70 mtorr. m.p.: 55° C. Anal. Calcd forC₁₆H₃₄N₄Ni: C, 56.34; H, 10.05; N, 16.42. Found: C, 55.22; H, 10.19; N,16.12.

EXAMPLE 9 Synthesis of bis(N,N′-diisopropylacetamidinato)manganese([Mn(^(i)Pr-AMD)₂]₂)

Following a similar procedure as described above for [Co(^(i)Pr-AMD)₂],but using MnCl₂, solid [Mn(^(i)Pr-AMD)₂]₂ was obtained as a product uponevaporation of the solvent from the hexanes extract. Yellowish greencrystals (79%). Sublimation: 65° C. at 50 mtorr. Anal. Calcd forC₃₂H₈N₆₈Mn₂: C, 56.96; H, 10.16; N, 16.61. Found: C, 57.33; H, 9.58; N,16.19.

EXAMPLE 10 Synthesis of manganese bis(N,N′-di-tert-butylacetamidinate)([Mn(^(t)Bu-AMD)₂])

Following a similar procedure as described above for [Mn(^(i)Pr-AMD)₂],but using 1,3-di-tert-butylcarbodiimide in place of1,3-diisopropylcarbodiimide, pale yellow crystals (87%) were obtained.Sublimation: 55° C. at 60 mtorr. m.p.: 100° C.

EXAMPLE 11 Synthesis of tris(N,N′-diisopropylacetamidinato)titanium([Ti(^(i)Pr-AMD)₃])

Following a similar procedure as described above for [La(^(i)Pr-AMD)₃],but using TiCl₃ in place of LaCl₃(THF)₂, [Ti(Pr-AMD)₃] was obtained as aproduct upon evaporation of the solvent from the hexanes extract. Browncrystals (70%). Sublimation: 70° C. at 50 mtorr. Anal. Calcd forC₂₄H₅₁N₆Ti: C, 61.13; H, 10.90; N, 17.82. Found: C, 60.22; H, 10.35; N,17.14.

EXAMPLE 12 Synthesis of tris(N,N′-diisopropylacetamidinato)vanadium([V(^(i)Pr-AMD)₃])

Following a similar procedure as described above for [Ti(Pr-AMD)₃], butusing VCl₃ in place of TiCl₃, [V(^(i)Pr-AMD)₃] was obtained as a productupon evaporation of the solvent from the hexanes extract. Red-brownpowder (80%). Sublimation: 70° C. at 45 mtorr.

EXAMPLE 13 Synthesis of silver (N,N′-di-isopropylacetamidinate)([Ag(^(i)Pr-AMD)]_(x) (x=2 and x=3)

These two compounds were prepared simultaneously in the same manner asdescribed for [Cu(^(i)Pr-AMD)], and obtained as a 1:1 mixture of dimerand trimer. Colorless crystals (90%). Sublimation: 80° C. at 40 mtorr.m.p.: 95° C. ¹H NMR (C₆D₆, 25° C.): 1.10 (d, dimer), 1.21 (d, trimer),1.74 (s, trimer), 1.76 (s, dimer), 3.52 (m, peaks for dimer and trimerare not well resolved.) Anal. Calcd for [C₈H₁₇N₂Ag].sub.x: C, 38.57; H,6.88; N, 11.25. Found: C, 38.62; H, 6.76; N, 11.34.

EXAMPLE 14 Atomic Layer Deposition of Copper Metal

The apparatus of FIG. 1 was used to deposit copper metal. Copper(I)N,N′-diisopropylacetamidinate dimer was placed in a stainless steelcontainer 11 with vapor volume 125 cubic centimeters and heated to 85°C., at which temperature it has a vapor pressure of about 0.15 Torr.Doses of 1.0 micromoles of the copper precursor were introduced bypressurizing the chamber to 10 Torr with nitrogen carrier gas. Hydrogenwas introduced in doses of 1.4 millimole using a gas-chromatographysampling valve. The area of the substrates 130 and the heated walls ofchamber 110 add up to about 10³ square centimeters. Thus, a dose ofcopper precursor was 1×10⁻⁹ moles/cm² and a dose of hydrogen was1.4×10⁻⁶ moles/cm². The “exposure” is defined as the product of thepartial pressure of a precursor vapor in the deposition zone and thetime that this vapor is in contact with a given point on the surface ofthe substrate. The exposure of the substrate to the copper precursor was2.3×10⁴ Langmuirs/cycle and its exposure to hydrogen was 3.4×10⁷Langmuirs/cycle.

One silicon substrate 130 was prepared by dissolving its native oxide byplacing it in dilute hydrofluoric acid solution for a few seconds. Nextthe substrate was irradiated by ultraviolet light (e.g. UV mercury lamp)in air until the surface became hydrophilic (about two minutes). Then asubstrate 130 was placed in chamber 110 and heated to a temperature of225° C. Another silicon substrate with narrow holes (4.5:1 ratio oflength to diameter) was treated similarly and placed in chamber 110.Substrates of glassy carbon were cleaned with 10% aq. HF (5 s),deionized water (30 s), and isopropanol (10 s) prior to drying and UVcleaning. Substrates of glass and sputtered platinum and copper onsilicon were cleaned with isopropanol (10 s) and dried.

Carrier gas flowed for 10 seconds between the alternating doses ofcopper precursor and hydrogen. 500 cycles were completed, and then theheater for the deposition chamber was turned off. After the substratescooled to room temperature, they were removed from the reactor. Thecarbon and silicon substrates were examined by Rutherford BackscatteringSpectroscopy and found to have a film of pure copper, 8×10¹⁶ atoms/cm²thick or 1.4×10⁻⁷ moles/cm² thick.

The silicon wafer with the holes was cleaved and a scanning electronmicrograph (SEM) was taken of a cross section of the holes. Themicrograph in FIG. 4 shows that copper coats the entire inside surfaceof the holes with aspect ratio (defined as the ratio of length todiameter) of about 10:1; thus this process for ALD of copperdemonstrates excellent step coverage.

EXAMPLE 15 Demonstration that the Surface Reactions are Self-Limited

Example 14 was repeated, except that the doses of both reactants weredoubled. The film thickness and its properties were unchanged from thoseof Example 1. This result shows that the surface reactions areself-limiting.

EXAMPLE 16 Demonstration that the Film Thickness Varies Linearly withthe Number of Cycles

Example 14 was repeated, except that 1000 cycles were used instead of500 cycles. Twice as much material was deposited. This result shows thateach self-limiting reaction reproduces the conditions needed for theother reaction to begin again, and that there are no significant delaysin initiating reactions or nucleating growth on the surface of thesubstrate.

EXAMPLE 17 Demonstration of a Range of Temperatures for Atomic LayerDeposition of Copper

Example 14 was repeated, except that the substrate temperatures werevaried within the range from 180° C. to 300° C. Similar results wereobtained, except that the thickness per cycle varied with temperature asshown in FIG. 6. At substrate temperatures below 180° C., no depositionof copper was observed. This observation shows that walls of a reactionchamber remain free of unwanted copper deposits if the wall temperatureis kept below 180° C. and above the dew point of the precursor.

EXAMPLE 18 Atomic Layer Deposition of Cobalt Metal

Example 14 was repeated, except that cobaltbis(N,N′-diisopropylacetamidinate) kept at 75° C. was used in place ofthe copper precursor and the substrate temperature was raised to 300° C.A silicon substrate previously coated with silicon dioxide and then withtungsten nitride was placed in the deposition chamber, along with afused silica capillary tube having inner diameter 20 micrometers. Ineach cycle, the dose of cobalt precursor was 4×10⁻⁹ moles/cm² and thedose of hydrogen was 9×10⁻⁷ moles/cm². The exposure of the substrates tothe cobalt precursor was 1×10⁵ Langmuirs/cycle and their exposure tohydrogen was 2×10⁷ Langmuirs/cycle.

The substrates were examined by Rutherford Backscattering Spectroscopyand found to have a film of pure cobalt metal, 5×10¹⁶ atoms/cm² thick or8×10⁻⁸ moles/cm² thick. The coated fused silica capillary was examinedby optical microscopy, which showed that the cobalt film extended to atleast 60 diameters (i.e. an aspect ratio>60) into the hole in thetubing. In FIG. 5, 1 points to the open end of the hole, and 2 shows howfar the coating penetrated into the hole. This result demonstrates theexcellent step coverage achieved by this process for ALD of cobalt.

EXAMPLE 19 Demonstration of a Range of Temperatures for Atomic LayerDeposition of Cobalt

Example 18 was repeated, except that the substrate temperature wasvaried between 250 and 350° C. Similar results were obtained, exceptthat the thickness per cycle varied with temperature as shown in FIG. 7.At substrate temperatures below 250° C., no deposition of cobalt wasobserved. This observation shows that walls of a reaction chamber remainfree of unwanted cobalt deposits if the wall temperature is kept below250° C. and above the dew point of the precursor.

EXAMPLE 20 Atomic Layer Deposition of an Adherent Copper Film on a Co/WNGlue Layer/Diffusion Barrier

The processes in Example 14 and Example 18 were repeated one after theother on a tungsten nitride (WN) layer previously coated onto silicondioxide, WN/SiO₂/Si. A smooth, adherent film with the multi-layerstructure Cu/Co/WN/SiO₂ was obtained. Adhesive tape was then applied tothe surface of this multi-layer structure. No loss of adhesion wasobserved when the tape was pulled off.

EXAMPLE 21 Atomic Layer Deposition of Cobalt Oxide

Example 18 was repeated, except that the hydrogen gas was replaced withwater vapor. A uniform, smooth layer of cobalt oxide with compositionapproximately CoO was deposited. Example 22. Atomic layer deposition ofmetallic nickel.

Example 14 was repeated, except that nickelbis(N,N′-diisopropylacetamidinate) kept at 75° C. was used in place ofthe copper precursor and the substrate temperature was raised to 280° C.A silicon substrate previously coated with silicon dioxide and then withtungsten nitride was placed in the deposition chamber. In each cycle,the dose of nickel precursor was 4×10⁻⁹ moles/cm² and the dose ofhydrogen was 8×10⁻⁷ moles/cm². The exposure of the substrates to thenickel precursor was 3×10⁴ Langmuirs/cycle and their exposure tohydrogen was 7×10⁶ Langmuirs/cycle.

The substrates were examined by Rutherford Backscattering Spectroscopyand found to have a film of pure nickel metal, 5×10¹⁶ atoms/cm² thick or8×10⁻⁸ moles/cm² thick.

EXAMPLE 23 Atomic Layer Deposition of Metallic Iron

Example 14 was repeated, except that ironbis(N,N′-di-tert-butylacetamidinate) kept at 75° C. was used in place ofthe copper precursor and the substrate temperature was raised to 280° C.A silicon substrate previously coated with silicon dioxide and then withtungsten nitride was placed in the deposition chamber. In each cycle,the dose of iron precursor was 4×10⁻⁹ moles/cm² and the dose of hydrogenwas 410⁻⁶ moles/cm². The exposure of the substrates to the ironprecursor was 8×10⁴ Langmuirs/cycle and their exposure to hydrogen was4×10⁷ Langmuirs/cycle.

The substrates were examined by Rutherford Backscattering Spectroscopyand found to have a film of pure iron metal, 5×10¹⁶ atoms/cm² thick or8×10⁻⁸ moles/cm² thick.

EXAMPLE 24 ALD of Iron Oxide

Example 21 was repeated, with bis(N,N′-di-tert-butylacetamidinato)iron([Fe(^(t)Bu-AMD)₂]) kept at 85° C. in place of cobaltbis(N,N′-diisopropylacetamidinate). In each cycle, the dose of ironprecursor was 4×10⁻⁹ moles/cm² and the dose of water vapor was 8×10⁻⁸moles/cm². The exposure of the substrates to the iron precursor was8×10⁴ Langmuirs/cycle and their exposure to water vapor was 7×10⁵Langmuirs/cycle. A uniform, smooth layer of iron oxide with compositionapproximately FeO was deposited on substrates heated to 250° C.

EXAMPLE 25 ALD of Lanthanum Oxide

Example 21 was repeated, withtris(N,N′-diisopropylacetamidinato)lanthanum ([La(^(i)Pr-AMD)₃]) kept at120° C. in place of cobalt bis(N,N′-diisopropylacetamidinate). In eachof 50 cycles, the dose of lanthanum precursor was 4×10⁻⁹ moles/cm² andthe dose of water vapor was 8×10⁻⁸ moles/cm². The exposure of thesubstrates to the lanthanum precursor was 3×10⁴ Langmuirs/cycle andtheir exposure to water vapor was 7×10⁵ Langmuirs/cycle. A uniform,smooth layer of lanthanum oxide about 5 nm thick, with compositionapproximately La₂O₃, was deposited on substrates heated to 300° C.

When the procedure of Example 21 was repeated with more than 50 cycles,the thickness was not uniformly distributed over samples in differentparts of the reaction chamber, and the thickness per cycle was largerthan 0.1 nm per cycle, particularly in the region near the exhaust tothe vacuum pump. It is our interpretation of this effect that watervapor was absorbed into the bulk of the thicker lanthanum oxide layerduring the water dose. During the few seconds of purge time followingthe water pulse some, but not all, of the adsorbed water was releasedback into the nitrogen gas and carried out of the chamber. However,further release of water vapor continued during the next dose oflanthanum precursor. Chemical vapor deposition of La₂O₃ then resultedfrom the reaction of this residual water vapor with the lanthanumprecursor, yielding a larger than expected growth rate, particularly inthe part of the deposition chamber closest to the exhaust to the vacuumpump. Uniform thickness could be restored by lengthening the purge timefor the water vapor. A more practical solution for restoring thethickness uniformity is described in Example 26.

EXAMPLE 26 ALD of Lanthanum Oxide/Aluminum Oxide Nanolaminate

Example 25 was repeated to deposit 16 cycles of lanthanum oxide. Then 6cycles of aluminum oxide were deposited by ALD using alternating dosesof trimethylaluminum vapor and water vapor, according to a processwell-known in the art. This pattern of (16 La₂O₃+6Al₂O₃) cycles wasrepeated 5 times. A uniform, smooth layer about 10 nm thick wasdeposited on substrates heated to 300° C. The layers had averagecomposition approximately LaAlO₃. Capacitors made of this material had adielectric constant about 18 and very low leakage current of about5×10⁻⁸ amperes per square centimeter at an applied potential of 1 volt.

Our interpretation of the thickness uniformity achieved in Example 26 isthat the aluminum oxide layers act as a barrier to diffusion of waterinto the lower layers of lanthanum oxide. Thus the thickness uniformityexpected of an ALD process is achieved for the La₂O₃/Al₂O₃ nanolaminatefor any desired thickness.

EXAMPLE 27 ALD of Manganese Oxide

Example 21 was repeated, with bis(N,N′-tert-butylacetamidinato)manganese([Mn(^(t)Bu-AMD)₂]) kept at 75° C. in place of cobaltbis(N,N′-diisopropylacetamidinate). In each cycle, the dose of manganeseprecursor was 4×10⁻⁹ moles/cm² and the dose of water vapor was 8×10⁻⁸moles/cm². The exposure of the substrates to the manganese precursor was3×10⁴ Langmuirs/cycle and their exposure to water vapor was 6×05Langmuirs/cycle. A uniform, smooth layer of manganese(II) oxide withcomposition approximately MnO was deposited on substrates heated to 250°C. at a deposition rate of about 0.1 nanometer per cycle.

EXAMPLE 28 ALD of Magnesium Oxide

Example 21 was repeated, with bis(N,N′-tert-butylacetamidinato)magnesium([Mg(^(t)Bu-AMD)₂]), prepared by a procedure similar to that describedin Example 3, kept at 80° C. in place of the cobaltbis(N,N′-diisopropylacetamidinate) used in Example 21. In each cycle,the dose of magnesium precursor was 3×10⁻⁹ moles/cm² and the dose ofwater vapor was 6×10⁻⁸ moles/cm². The exposure of the substrates to themagnesium precursor was 3×10⁴ Langmuirs/cycle and their exposure towater vapor was 5×10⁵ Langmuirs/cycle. A uniform, smooth layer ofmagnesium oxide with composition approximately MgO was deposited onsubstrates heated to 250° C. at a deposition rate of 0.08 nanometer percycle.

EXAMPLE 29 Synthesis of Lithium N,N′-di-sec-butylacetamidinate

One equivalent of dry sec-butylamine, one equivalent of dry acetonitrileand 0.02 equivalents of lanthanum triflate, a catalyst, were placed intoa Schlenk flask with a reflux condenser. Dry nitrogen was passed slowlyinto the flask, up through a reflux column and out of an oil bubblerwhile the reaction mixture refluxed for 3 days. Excess reactants werethen removed under vacuum and the remaining liquid was purified bydistillation to sec-butylacetamidine. ¹H NMR (C₆D₆, 25° C.): δ1.49 (m,4H), δ1.38 (s, 3H), δ1.11 (d, J=6 Hz, 6H), δ0.90 (t, J=8 Hz, 6H).

An ether solution of sec-butylacetamidine was prepared at aconcentration of 1 gram per 10 ml of dry ether in a reaction flask witha reflux column and an oil bubbler. One equivalent of methyl lithiumsolution in ether was then added slowly to the sec-butylacetamidinesolution and the reaction mixture was stirred for an hour. The resultingsolution of lithium N,N′-di-sec-butylacetamidinate was then used withoutfurther purification for the synthesis of other metalsec-butylacetamidinate salts. ¹H NMR (C₆D₆, 25° C.) for lithiumN,N′-di-sec-butylacetamidinate: δ3.16 (m, 2H), 81.71 (s, 3H), δ1.68 (m,2H), δ1.52 (m, 2H), δ1.19 (d, J=6 Hz, 4H), δ0.94 (m, 6H).

EXAMPLE 30 Synthesis of cobalt bis(N,N′-di-sec-butylacetamidinate)([Co(sec-Bu-AMD)₂])

Anhydrous cobalt(II) chloride, CoCl₂, was weighed into a Schlenk flaskin a dry box. Two equivalents of the lithiumN,N′-di-sec-butylacetamidinate solution prepared in Example 29 areadded, along with an equal volume of dry THF. The reaction mixture wasstirred overnight, and then the volatiles were removed under vacuum atroom temperature. The solid was dissolved in dry hexanes, filtered, andthe hexanes removed from the filtrate under vacuum at room temperatureto give a crude yield of 82% of cobaltbis(N,N′-di-sec-butylacetamidinate). This liquid was purified bydistillation (55° C. at 60 mtorr).

EXAMPLE 31 Synthesis of copper(I) N,N′-di-sec-butylacetamidinate dimer([Cu(sec-Bu-AMD)]₂)

The procedure of Example 30 was used with one equivalent of copper (I)chloride, CuCl, in place of the cobalt chloride and one equivalent ofthe lithium N,N′-di-sec-butylacetamidinate prepared in Example 29.[Cu(sec-Bu-AMD)]₂ was isolated by the procedure of Example 30.Sublimation: 55° C. at 50 mtorr. mp. 77° C. [Cu(sec-Bu-AMD)]₂ has anadvantage as a precursor for ALD of copper in that it is a liquid at thetemperature used for vaporization (about 100° C.), resulting in morereproducible delivery of vapor than was obtained by sublimation of solidprecursors.

EXAMPLE 32 Synthesis of bismuth tris(N,N′-di-tert-butylacetamidinate)dimer ([Bi(^(t)Bu-AMD)₃]₂)

One equivalent of bismuth trichloride, BiCl₃, and three equivalents oflithium N,N′-di-tert-butylacetamidinate (obtained by reaction of1,3-di-tert-butylcarbodiimide with methyllithium) were refluxedovernight in THF. After the evaporation of the THF, extraction in dryhexanes, filtration and evaporation of the hexanes from the filtrate,the crude product was isolated by sublimation (70° C. at 80 mtorr).m.p.: 95° C. Dimeric by cryoscopy in p-xylene solution.

EXAMPLE 33 Synthesis of strontium bis(N,N′-di-tert-butylacetamidinate)([Sr(^(t)Bu-AMD)₂]_(n))

Following a procedure similar to that used in Example 32, strontiumbis(N,N′-di-tert-butylacetamidinate) was obtained. The crude product waspurified by sublimation (13° C. at 90 mtorr).

EXAMPLE 34 ALD of Bismuth Oxide, Bi₂O₃

Following a procedure similar to Example 25, films of bismuth oxide,Bi₂O₃, were deposited on substrates at a temperature of 200° C. from avapor source containing bismuth tris(N,N′-di-tert-butylacetamidinate) at85° C. The thickness of the films was about 0.03 nanometers per cycle.

EXAMPLE 35 Synthesis of tris(N,N′-diisopropylacetamidinato)ruthenium([Ru(^(i)Pr-AMD)₃])

Following a procedure similar to Example 11,tris(N,N′-diisopropylacetamidinato)-ruthenium ([Ru(^(i)Pr-AMD)₃]) wasobtained in low yield.

COMPARATIVE EXAMPLE 1

Example 14 was repeated using only the copper precursor, and no hydrogengas. No film was observed to have been deposited on the substratesurface.

COMPARATIVE EXAMPLE 2

Example 18 was repeated using only the cobalt precursor, and nohydrogen. No film was observed to have been deposited on the substratesurface.

Those skilled in the art will recognize or be able to ascertain using nomore than routine experimentation, many equivalents to the specificembodiments of the invention described specifically herein. Suchequivalents are intended to be encompassed within the scope of thefollowing claims.

What is claimed is:
 1. A compound represented by the general formula fora dimer

or oligomers of the monomeric unit, wherein M is selected from themetals copper, silver, gold, and iridium, and wherein R¹, R^(1′), R²,and R^(2′) independently represent alkyl groups, alkenyl groups, alkynylgroups, trialkylsilyl groups, or other non-metal atoms or groups thatare not aryl, and R³ and R^(3′) independently represent hydrogen, alkylgroups, alkenyl groups, alkynyl groups, trialkylsilyl groups, or othernon-metal atoms or groups that are not aryl.
 2. A compound as claimed inclaim 1, having the chemical structural formula


3. The compound as claimed in claim 1, wherein at least one of R¹,R^(1′), R², R², R³ and R^(3′) represent unsubstituted alkyl groups. 4.The compound as claimed in claim 1, wherein at least one of R¹, R^(1′),R², R², R³ and R^(3′) represent fluoroalkyl groups.
 5. The compound asclaimed in claim 1, wherein M is copper.
 6. The compound as claimed inclaim 1, wherein R¹, R^(1′), R², and R^(2′) independently representalkyl groups, alkenyl groups, alkynyl groups, or trialkylsilyl groups,and R³ and R^(3′) independently represent hydrogen, alkyl groups,alkenyl groups, alkynyl groups, or trialkylsilyl groups.
 7. A compoundrepresented by the general formula for a dimer

or oligomers of the monomeric unit, wherein M is lithium or sodium, andwherein R¹, R^(1′), R², and R^(2′) independently represent alkyl groups,alkenyl groups, alkynyl groups, trialkylsilyl groups, or other non-metalatoms or groups that are not aryl, and R³ and R^(3′) independentlyrepresent hydrogen, alkyl groups, alkenyl groups, or alkynyl groups, butexcluding R³ and R^(3′) that are methyl, n-butyl, or tert-butyl when Mis lithium.
 8. The compound as claimed in claim 7, wherein R¹, R^(1′),R², and R^(2′) independently represent alkyl groups, alkenyl groups,alkynyl groups, or trialkylsilyl groups, and R³ and R^(3′) independentlyrepresent hydrogen, alkyl groups, alkenyl groups, or alkynyl groups, butexcluding R³ and R^(3′) that are methyl, n-butyl, or tert-butyl.
 9. Thecompound of claim 7, wherein R³ and R^(3′) are independently selectedfrom the group consisting of hydrogen, ethyl, n-propyl, isopropyl, andsec-butyl groups.
 10. A process for depositing a material comprising ametal, M, the process comprising exposing a vapor of a first reagent toa substrate, wherein the reagent comprises a compound represented by thegeneral formula for a dimer

or oligomers of the monomeric unit, wherein M is selected from themetals copper, silver, gold, iridium, lithium, and sodium, and whereinR¹, R^(1′), R², and R^(2′) independently represent alkyl groups, alkenylgroups, alkynyl groups, trialkylsilyl groups, or other non-metal atomsor groups, and R³ and R^(3′) independently represent hydrogen, alkylgroups, alkenyl groups, alkynyl groups, trialkylsilyl groups, or othernon-metal atoms or groups, but excluding (i) R³ and R^(3′) that aremethyl, n-butyl, or tert-butyl when M is lithium and (ii) R³ and R^(3′)that are trialkylsilyl when M is lithium or sodium.
 11. The process ofclaim 10, further comprising exposing a vapor of a second reagent to thesubstrate.
 12. The process of claim 11, wherein the second reagent is areducing gas, a nitrogen-containing gas, or an oxygen containing-gas.13. The process of claim 12, wherein the reducing gas is hydrogen. 14.The process of claim 12, wherein the nitrogen-containing gas is ammonia.15. The process of claim 12, wherein the oxygen-containing gas compriseswater.
 16. The process of claim 11, wherein said exposing a vapor of asecond reagent is carried out after said exposing a vapor of a firstreagent.
 17. The process of claim 16, wherein the second reagent is areducing gas, a nitrogen-containing gas, or an oxygen containing-gas.18. The process of claim 17, wherein the reducing gas is hydrogen. 19.The process of claim 17, wherein the nitrogen-containing gas is ammonia.20. The process of claim 17, wherein the oxygen-containing gas compriseswater.
 21. The process of claim 10, wherein R¹, R^(1′), R², and R^(2′)independently represent alkyl groups, alkenyl groups, alkynyl groups, ortrialkylsilyl groups, and R³ and R^(3′) independently representhydrogen, alkyl groups, alkenyl groups, alkynyl groups, or trialkylsilylgroups.
 22. The process of claim 10, wherein M is copper.
 23. Thecompound as claimed in claim 7, wherein at least one of R¹, R^(1′), R²,R², R³ and R^(3′) represent fluoroalkyl groups.
 24. The compound asclaimed in claim 7, wherein R¹, R^(1′), R², and R^(2′) independentlyrepresent fluoroalkyl groups, alkenyl groups, alkynyl groups,trialkylsilyl groups, and R³ and R^(3′) independently representhydrogen, fluoroalkyl groups, alkenyl groups, alkynyl groups.
 25. Theprocess as claimed in claim 10, wherein at least one of R¹, R^(1′), R²,R², R³ and R^(3′) represent fluoroalkyl groups.